Sydney: Speech patterns can reveal the severity of depression as well as a patient's response to treatment, suggests a new study.

The study, the largest of its kind in the world, found that improvement in patients diagnosed with depression and undergoing treatment can be monitored over the phone by looking at changes in their speech.

Adam Vogel, who heads the Speech Neuroscience Unit at Australia's University of Melbourne, said speech was a strong marker of brain health, and changes in how we sound reflected how well our brain was working, the journal Biological Psychiatry reports.

"The speech of people with depression changes when they respond to treatment, becoming faster and with shorter pauses. Those with more severe depression produce longer pauses and have slower speaking rates," Vogel said, according to a Melbourne statement.

He randomised controlled trial of 105 patients looked at vocal acoustic properties such as timing, pitch and intonation to see if they could provide reliable biomarkers to depression severity and responses to treatment.

Patients were required to call an automated telephone system and leave samples of their speech, such as saying how they felt, reading a passage of text and reciting the alphabet.

"This offers greater treatment flexibility as we can now check on our patients remotely, looking at their speech patterns even from remote or rural areas," said James Mundt, senior research scientist at the Centre for Psychological Consultation in Wisconsin, US, who collaborated with Vogel."

We know that depressed patients have difficulties expressing themselves, so if we can improve how we assess depression, then we can improve how we treat it," added Mundt.